AUTHOR=Ohara Shizuka , Yano Ryoko , Furuya Kenichiro , Sato Takafumi , Ikeda Syunichiro , Koike Kazuhiko 

TITLE=The effects of sea-bottom plowing on phytoplankton assemblages: a case study of northern Hiroshima Bay, the Seto Inland Sea of Japan

JOURNAL=Frontiers in Marine Science

VOLUME=Volume 10 - 2023

YEAR=2023

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2023.1222810

DOI=10.3389/fmars.2023.1222810

ISSN=2296-7745

ABSTRACT=Sea-bottom plowing is originally a method to oxidize sediment by stirring the bottom with a trawl fishing tool, and its effect on increase primary productivity of the water column was investigated in the western part of the Seto Inland Sea of Japan. Preliminary field sampling showed diatom resting stage cells were abundant in the sediment of the tested area at 1.5-2.6 × 10 5 MPN g -1 wet sediment. When the sediment was added to filtered seawater, diatom cells emerged from the sediment after one day and increased more drastically under a light level corresponding to sunny weather than cloudy weather. In the actual trials of sea-bottom plowing at the field in continuous four years, dissolved inorganic nutrients increased at the bottom layer after the plowing and promoted photosynthetic activities of the phytoplankton communities in 2018 and 2021. Chlorophyll a concentrations at the middle layers increased 1.06-2.15 times after the plowing throughout the trials for four years. Diatoms contributed 67-99% of these chlorophyll a increases and included the genera Skeletonema and Chaetoceros, which formed resting stage cells in the sediment. Pseudo-nitzschia spp. often increased after the plowing, which were assumed to be seawater origin. Estimated primary productivities of the middle layers once dropped in the following day due to turbid water caused by the plowing but increased 2.03-4.41 times after two or five days in 2018, 2019 and 2021. These results suggest that sea-bottom plowing has an enrichment effect on diatoms and could be a possible measure to fertilize the sea.